Nanotubes Show Promise From TVs To Velcro

Enter the bucky ball's illegitimate son, the nanotube.

Nanotubes, once considered the waste material that sat at the bottom of chambers used for making bucky balls, are being looked at with newfound respect by physicists, electrical engineers, and computer and materials scientists. What's more, their applications seem to be growing as fast as the nanotubes themselves, such as:

* Television the depth of a framed print that uses far less power than present-day FED's, where silicon does the electron-emitting.

* Nano-memory: Computer memory that's 1,000 times smaller than what currently is possible.

* Nano-Velcro: which could be 100 times stronger, and 10 times lighter, than steel.

Nanotubes are not a new form of carbon; they combine the molecular configurations of graphite and bucky balls, taking advantage of the properties of both. The tube is formed when two ends of graphite join together--like chicken wire around a post--and half a bucky ball attaches at each end. Although nanotubes could feasibly grow to lengths ad infinitum, the simplest model looks something like a quilted cold capsule.

"The synthesis of bucky balls and nanotubes generally produce very small quantities," explains David Tomanek, professor of physics at Michigan State. He and electrical and computer engineers Virginia Ayres and Dean Aslam are embarking on a project to grow and study nanotubes for use in consumer-related applications.

Ayres and Aslam extol the virtues of both diamonds and nanotubes, proposing that, in some cases, a diamond--nanotube hybrid might be the best bet. Such is the case with field emission displays (FED), also referred to as flat-panel displays, a new technology that could revolutionize the way televisions are manufactured.

The reason a television currently occupies so much space in the living room is because three electron guns are firing electrons from the back, line by line, at individual pixels on the screen. Electrons hit the phosphor pixels, and, wham! Homer Simpson is yelling at Bart. Applied to FED technology, molecule-sized nanotubes would emit the electrons instead of the electron guns, with the precision of one nanotube per pixel. The result would be a television the depth of a framed print that, if Ayres and Aslam have it their way, uses far less power than present-day FED's, where silicon does the electron-emitting.

A material's ability to emit electrons is defined by two things: one, the electrical field at the surface (the number of electrons that are buzzing around), and two, the amount of work required to coax the electrons out, called the work function.

Aslam says that for materials with high work functions, like silicon or most metals, sharp edges must be formed to amplify the electrical field at the tip. "If you use a material that has almost zero work function--and that's diamond--then you don't have to make a tip," he says. "But," he adds, "if you can make a tip on top of that..."

"Better still!" Ayres said. "This is a good thing because to generate the field that takes the electrons out, we need a power supply; so one of the things that we want to do is reduce that power supply requirement. Otherwise, we have a thin screen, but an enormous, massive power supply. We've defeated our purpose."

For their project, Ayres will be studying the fine line that exists between diamonds and nanotubes by examining the conditions necessary for their growth. Aslam will be conducting the field-emission studies and examining some of the most pervasive questions, namely what is the principal electron-emitting mechanism, and why is emission from diamond, though low in work function, non-uniform in pattern? Tomanek will perform the computer modeling. The three are collaborating with DuPont and NASA Goddard Space Center in their research.

In addition to their use in field emission displays, nanotubes show promise for other applications, says Richard Enbody, associate professor of computer science and engineering. He and Tomanek have applied for two patents that make creative use out of several of the extraordinary properties of nanotubes: nano-memory and nano-Velcro.

"Since all computers are based on the binary system, they only have two states: you can call one of the states 'zero' and one of them 'one,'" explains Enbody. "Therefore, any computer memory, whether it's on a CD ROM, or floppy disk, or hard drive, or RAM, has two states: on and off--zero and one. That's the whole basis for computer memories."

Enbody and Tomanek reason that by putting a bucky ball inside a nanotube, and by getting the bucky ball to slide from one end, the "zero" state, to the other, the "one" state, computer memory could be derived at the smallest known scale.

"This has the potential of making a memory that's 1,000 times smaller than what we have," Enbody said.

Enbody and Tomanek's other idea, nano-Velcro, or the micro-fastener system, makes use of the inimitable strength of nanotubes, 100 times stronger (and ten times lighter) than steel, and its temperature-resistance, up to 3,000 degrees Kelvin (nearly 5,000 degrees Fahrenheit). They are proposing a hook and loop system, similar to the Velcro flap on a tennis shoe, that uses nanotubes instead. To Enbody and Tomanek, nano-Velcro could be used to manufacture anything--from space shuttles to micro-robots--and would require the same force necessary to form diamond to pull the two sides apart.

"This is about research, Tomanek said. "This is about the next century. This is where we are going."